Acetabular revision of total hip replacements (THR) is one of the most challenging problems in orthopedic surgery today. Despite great advances in imaging, preoperative visualization and assessment of even the most difficult cases is still performed just like the first revision over forty years ago, using subjective examination of anteroposterior (AP) radiographs. This presents an opportunity for improving clinical out-come, especially given the widely-held orthopaedic surgery tenet that clinical success is directly related to the thoroughness and accuracy of preoperative planning. Ideally, revision surgical planning should determine defect type, describe amount and location of remaining bone (to select the best mechanically-sound reconstruction option), and confirm whether reconstruction should be performed. Lack of a validated, quantitative assessment that provides structural information limits the usefulness of current systems and leads to worse clinical outcomes, added cost, and wide intra- and inter-surgeon variability in selecting reconstruction options. Therefore, the next step for biomedical imaging is to move beyond outdated radiograph-based evaluations and onto mechanically and clinically relevant structural imaging. Our goal is to replace conventional radiograph-based planning with structural imaging in order to guide surgical reconstruction and improve the clinical outcomes of individuals with deficient acetabular bone. Our broad hypothesis is that advanced CT techniques increase the predictive power of preoperative assessments, link defect type with mechanical effects, and improve clinical outcomes. We seek to develop image-guided techniques that are mechanically-relevant and based on existing imaging technologies. This R21 proposal's specific aim is: Aim 1: Develop and validate objective CT-based structural-imaging techniques to guide surgery by describing host bone and its mechanical environment. Hypothesis: CT-based structural-imaging accurately (+ 2mm linear measurements, + 3% volume measurements, <15 % bone density errors) and reliably (inter-observer, kappa >0.80) define 3D structure and mechanical consequence. Future research aims include clinical implementation, outcome and cost benefit analyses, and development of minimally invasive surgery. Completion of this project will create an accurate CT-based technique to guide surgery by structurally assessing the morphology, density, and mechanics of the deficient acetabulae. This is the first and important step toward improving surgical planning, execution, and clinical outcomes of these difficult cases.